This invention relates generally to imaging arrays, and more particularly, to pixel formations for imaging arrays.
Imaging arrays typically include a photosensor array coupled to a scintillating medium. Radiation absorbed in the scintillator generates optical photons which in turn pass into a photosensor, such as a photodiode. The photon is absorbed in the photosensor and an electrical signal corresponding to an incident photon flux is generated. Hydrogenated amorphous silicon (a-Si:H) is commonly used in the fabrication of photosensors due to advantageous photoelectric characteristics of a-Si:H and a relative ease of fabricating such devices. In particular, photosensitive elements, such as photodiodes, can be formed in connection with necessary control or switching elements, such as thin film transistors (TFTs), in a relatively large array. Radiation detectors and display arrays are typically fabricated on a large substrate on which many components, including TFTs, address lines, capacitors, and devices such as photosensors, are formed through the deposition and patterning of layers of conductive, semiconductive, and insulative materials.
At least one known fabrication process for such a TFT array typically includes fabricating a bottom gate TFT and data and scan address lines. In some known bottom gate TFT""s, the bottom gate metal shields a channel region, i.e. acts as a light blocking element, blocking light from a back light. The light blocking layer is desirable since photons can create an undesirable leakage in the TFT. For example, in a digital X-ray panel, the light is created from the scintillator that is deposited on the top of the devices, therefore the TFT regions are directly exposed to the photons. Therefore, an additional light blocking layer, requiring an additional photolithography level, is therefore necessary to shield the TFT channel region from undesirable light.
In one aspect, a radiation detector is provided. The radiation detector includes a top gate thin film transistor (TFT) including a source electrode, a drain electrode, a gate electrode, a TFT dielectric layer, a TFT semiconductive layer, and a TFT intrinsic amorphous silicon (a-Si) layer. The radiation detector also includes a capacitor including a first electrode, a second electrode substantially coplanar with the gate electrode, and a capacitor dielectric, the capacitor dielectric including a capacitor dielectric layer substantially coplanar with the TFT dielectric layer, a capacitor semiconductive layer substantially coplanar with the TFT semiconductive layer, and a capacitor a-Si layer substantially coplanar with the TFT a-Si layer.
In another aspect, a method for fabricating a radiation detector is provided. The method includes forming a top gate thin film transistor (TFT) including a source electrode, a drain electrode, a gate electrode, a TFT dielectric layer, a TFT semiconductive layer, and an a-Si layer, and forming a capacitor including a first electrode, a second electrode substantially coplanar with the gate electrode, and a capacitor dielectric, the capacitor dielectric comprising a capacitor dielectric layer substantially coplanar with the TFT dielectric layer, a capacitor semiconductive layer substantially coplanar with the TFT semiconductive layer, and a capacitor a-Si layer substantially coplanar with the TFT a-Si layer.
In a further aspect, an imaging system including a radiation source and a radiation detector is provided. The radiation detector includes a top gate thin film transistor (TFT) including a source electrode, a drain electrode, a gate electrode, a TFT dielectric layer, a TFT semiconductive layer, and a TFT intrinsic amorphous silicon (a-Si) layer. The radiation detector also includes a capacitor including a first electrode, a second electrode substantially coplanar with the gate electrode, and a capacitor dielectric, the capacitor dielectric including a capacitor dielectric layer substantially coplanar with the TFT dielectric layer, a capacitor semiconductive layer substantially coplanar with the TFT semiconductive layer, and a capacitor a-Si layer substantially coplanar with the TFT a-Si layer.
In a still further aspect, a method for fabricating a radiation detector is provided. The method includes, forming a capacitor second electrode and a gate electrode in a single process step, forming a capacitor dielectric and a TFT dielectric layer in a single process step, and forming a capacitor semiconductor layer and a TFT semiconductive layer in a single process step.